Bodyboards and surf board as well as other buoyant boards used in water sports are normally composed of a laminated structure in which a center core has joined to it a top deck skin and a bottom skin. The sides of the boards may include a rail and a chine. Typically, the thickness of the board is about 21/2 inches in the major area of the board. As is well known in the case of bodyboards, there are a variety of configurations such as a tail configuration and the nose configuration. Flutes may be provided in the bottom surface of the board.
In general, bodyboards may include a variable flexure characteristic, e.g., needed flexure in the nose area for what is known as "power turns" and strength in the mid and tail sections which may be required for speed. The nose section may be configured to permit corner flexing or flexing along the entire nose section. In general, the bottom skin is smooth, tough and scratch resistant for speed over the water. The deck skin or upper surface of the board is textured to provide relative slip resistance. It is also generally true that lighter weight in a board is desired since a lighter weight board will displace less water resulting in increased speed, the latter a desirable characteristic. It is also the case that strength and resistance to delamination are required. The salt water environment in which these boards are generally used and the sometimes severe maneuvers which are accomplished on the board require that the board be Well Constructed to last for a reasonable period of desired use and reliable performance.
In addition to the above, there is a characteristic of a bodyboard known as "rocker". This generally refers to the bending up from the centerline of the bodyboard. There is overall rocker, nose rocker and tail rocker. Rocker usually affects the ability of the board to plane above the uneven surface of the water. It also affects the speed of the board, the ability to do "360's" (spinning the board like a top), and other control characteristics of a board. There is no "perfect" rocker but there is general agreement on what constitutes a good rocker. Typically good rocker involves a gentle curve upward from about 1/3 back from the nose with a resulting rise from the bottom of the board to about 11/2 inches at the nose. The other 2/3 of the board should be flat or have a very small amount of rise from about 1/3 back from the nose.
In recent years, the use of closed pore polypropylene foam as a core material for bodyboards has become increasingly popular. One of the problems in using polypropylene foam as a core is the difficulty in joining other components to the core. In large part the difficulty stems from the desire to laminate to the core a polymer that is different from polypropylene in order to obtain specific characteristics in the finished board product. Typically, the polymer joined to the polypropylene core is a material such as polyethylene in a closed pore thin foam textured layer as the top or deck skin while a film (non-porous and smooth) of polyethylene is used as the bottom skin. The bottom skin should preferably offer crease resistance since in use the board is sometimes flexed along the long axis of the board. Overall, it is desirable to permit the bodyboard to deflect and to return its energy quickly, i.e., a spring action.
It has been the practice in using polypropylene foam as the core to use a liquid glue or adhesive to join other components to the core material. The difficulty with such a procedure is that chemical vapors are released into the air as the solvent for the adhesive evaporates during the manufacturing process. Another problem is that the use of adhesive may add considerable weight to the board where the objective is to provide a relatively low weight for better board performance. Still another objection is the action of salt water on the adhesive joint with possible delamination in local areas or along a section of the board.
Another prior art procedure for joining other materials to the polypropylene foam core is to use a heat lamination process. To understand the problems associated with this prior art process, it is helpful to understand better the nature of the polypropylene foam. Polypropylene foam is usually made by one of two processes, one called a resilient molded bead process and the other an extruded bead process. In the extruded bead process, the polypropylene resin starts in the form of solid pellets. They are then melted and mixed with other chemicals. The molten mixture is then extruded, usually in the form of a sheet. The sheet is then foamed either by activating chemical in the material or by gaseous injection. The extruded foam is comprised of closed cells. The resilient molded bead process is also known as steam chest molding in which the beads are placed in a mold and expanded through the use of steam and pressure.
For example, if one examines a direct heat laminated combination of a polypropylene closed cell foam and a sheet of polyethylene film, several deficiencies become apparent. One such condition is what is known as "foam tear", a term used to describe a joint which is stronger than one or both of the materials joined together. The objective is to achieve foam tear i.e. parting of one or more of the laminated materials rather than separation at the bond line. This is sometimes referred to as peel strength, i.e., the strength of the bond is greater than the tear strength of the materials laminated together, in other words, if one attempts to pull the heat laminated materials apart, the foam layer will tear rather than permitting delamination along the bond line. For practical reasons, polyethylene and polypropylene do not heat laminate together well enough to achieve foam tear.
Another deficiency is that the prior art practices have resulted in "puckering" or shrinking of the layer, rather than a smooth even surface. This results in a considerable amount of scrap and inferior bonding. While it is possible to heat laminate polyethylene and a polypropylene foam material together, extremely close temperature control is necessary if one is to achieve foam tear. For example, polyethylene may be heat laminated to polyethylene at about 229 degrees F., polypropylene may be heat laminated to polypropylene at about 290 degrees F., achieving foam tear in each case. However, in heat laminating polyethylene to polypropylene foam, temperatures as high as and in excess of 500 degrees F. have been used with the result of considerable shrinking and without achieving foam tear. It is apparent that it is not the temperature used in heat lamination which is the sole cause of the problem; it seems to be related to the polymeric differences. Even the addition of chemicals to the host polymer to change the melting points did not seem to solve the heat lamination problem.
It is accordingly apparent that a need exists for an improved laminated buoyant foam structure in which the laminated parts are firmly and adequately bonded together, especially if the materials to be bonded are of different polymeric materials or of different foam characteristics.
It is also apparent that in the case of foam products use in water sports, for example, bodyboards and surf boards and the like, that a need exists for a laminated product which has strength, flexibility and return of energy as desired, and which will not delaminate over the useful and normal life of the product.
It is also apparent that a need exists for a more reliable and less expensive procedure for the commercial manufacture of foam products for use in water sports, for example, bodyboards and surf boards and the like which results in simplified and more effective and less expensive procedures for the commercial manufacture of such products
Equally apparent is that a need exists for a simplified construction of buoyant foam products for use in water sports, for example, bodyboards and surf boards and the like, in which the resulting product provides the desired strength and flexibility and in which the layers of material bonded to the foam core are securely anchored to prevent delamination.
Moreover, it is apparent that a need exists for an improved foam product for use in water sports in which a top and bottom skin is joined to the foam core and in which the peel strength of the bond between the top layer and the foam and between the bottom layer and the foam is greater than the tear strength of the top and bottom layers and the foam.